Coronary bypass surgery commonly requires a length of the saphenous vein of the patient to form a shunting vessel around a site of stenosis or other blockage in a coronary artery. The saphenous vein was conventionally ‘harvested’ from the patient's leg through an incision extending the length of the section of saphenous vein to be harvested. Recently, endoscopic surgical procedures have replaced open-incision harvesting procedures and have significantly reduced patient trauma, discomfort, complication and recovery time. Specifically, contemporary vein-harvesting procedures require only a small incision over the saphenous vein to expose the vein, and then blunt tissue dissection is performed along the length of the vein using an elongated endoscopic cannula inserted through the incision to detach the vein and lateral branch vessels from connective tissue along the length of the vein to be harvested. The channel or anatomical space thus formed within the bluntly dissected tissue along the course of the vessel may be expanded to provide additional space within which to perform associated surgical procedures such as clipping and ligating lateral branch vessels using mechanical retractors inserted within the channel to elevate tissue away from the vein being harvested.
Alternatively, the channel or anatomical space formed along the course of the vessel may be retained in expanded condition by insufflating the channel with gas under pressure. The gas may be supplied through an access port which admits endoscopic instruments through a sliding gas-tight seal that is inserted into and sealed within the small initial incision over the saphenous vein. Conventional access ports commonly include a hollow body with an expandable peripheral balloon disposed about the outer distal end of the body, and with one or more diaphragm-type sliding seals disposed at the proximal end across the central bore of the hollow body. In operation, such conventional access port is inserted into a small incision and the peripheral balloon is then inflated to seal the port within the incision. Gas under pressure may then be supplied through the access port as elongated endoscopic instruments are inserted, and manipulated through the sliding seal during surgical procedures within the anatomical space formed along the vein, without significant loss of gas pressure within the anatomical space during insertions and removals of surgical instruments through the sliding seal of the access port. For convenience, the hollow body may include multiple sliding gas seals that are selectively positioned on the proximal end of the port to accommodate a selection of elongated instruments of different diameters passing through the central bore of the hollow body. Such access ports include a flapper valve to inhibit outflow of gas therethrough as an elongated instrument is withdrawn from the central bore. However, the versatility of selectable seals and flapper valves to accommodate endoscopic instruments of various diameters significantly extends the length of the hollow body and requires additional manual re-configuration to position a selected seal over the proximal end of the hollow body to provide a sliding seal of appropriate dimensions to accommodate the diameter of a selected endoscopic instrument.